hip

Anatomically, the hip is a joint rather than a region. When we speak of someone having "broad hips" we really mean the hip bones and their covering of muscles, fat and skin. The hip is a synovial joint between the head of the femur and the acetabulum on the side of the hip bone; structurally it is a "ball-and-socket" joint.

The hip is normally an extremely stable joint, even though it is capable of a wide range of movement.

Stability is conferred by:

The excellent bony fit between the round head of the femur (approximately 2/3 of a sphere) and the deep acetabulum. The acetabulum is made still deeper and more efficient by a rim of fibrocartilage - the labrum - which runs around the circumference.
The capsule. This forms a strong fibrous sleeve around the joint. It is attached around the margins of the acetabulum and to the neck of the femur (posteriorly) and the intertrochanteric line of the femur (anteriorly). It has specialised thickenings (the ilio-, ischio- and pubofemoral ligaments) which are arranged in a spiral and which, when tight, help to secure the head of the femur in the acetabulum. Some have more particular roles, e.g. the iliofemoral ligament helps to resist hyperextension at the joint i.e. the trunk falling backwards on the femoral heads.
The surrounding muscle mass, which is thick and powerful

The hip is capable of a series of pairs of movements. These include :-

flexion (the limb is moved forwards and upwards) and extension (the limb is moved backwards and downwards)
abduction (the limb is moved outwards and upwards) and adduction (the limb is moved inwards and downwards)
medial rotation (the whole limb is twisted so that the big toe faces inwards towards the mid-line) and lateral rotation (it is twisted so that the big toe faces outwards away from the mid-line).

These movements, and the muscles which produce them, are discussed in detail in the HIP TUTORIAL.